Antiphagocytic Function Research Articles

Nucleotide sequences of two adjacent M or M-like protein genes of group A streptococci: different RNA transcript levels and identification of a unique immunoglobulin A-binding protein.

M protein is a key virulence factor present on the surface of group A streptococci. M protein is defined by its antiphagocytic function, whereas M-like proteins, while structurally related to M proteins, lack an established antiphagocytic function. Group A streptococci can be divided into two main groups (class I and II) on the basis of the presence or absence of certain antigenic epitopes within the M and M-like molecules, and importantly, the two classes correlate with the disease-causing potential of group A streptococci. In an effort to better understand this family of molecules, a 2.8-kb region containing the two M protein-like genes from a class II isolate (serotype 2) was cloned and sequenced. The two genes lie adjacent to one another on the chromosome, separated by 211 bp, and have many structural features in common. The emmL2.1-derived product (ML2.1 protein) is immunoreactive with type-specific antiserum, a property associated with M proteins. The cloned product of the downstream gene, emmL2.2 (ML2.2 protein), is an immunoglobulin A (IgA)-binding protein, binding human myeloma IgA. Interestingly, the RNA transcript levels of emmL2.1 exceed that of emmL2.2 by at least 32-fold. Northern (RNA) hybridization and primer extension studies suggest that the RNA transcripts of emmL2.1 and emmL2.2 are monocistronic. The ML2.1 and ML2.2 proteins exhibit 53% amino acid sequence identity and differ primarily in their amino termini and peptidoglycan-spanning domains and in a Glu-Gln-rich region present only in the ML2.1 protein. However, the previously described M-like, IgA-binding protein from a serotype 4 isolate (Arp4) displays a higher level of amino acid sequence homology with the ML2.1 molecule than with the IgA-binding ML2.2 protein. Amino acid sequence alignments between all M and M-like proteins characterized to date suggest the existence of two fundamental M or M-like gene subclasses within class II organisms, represented by emmL2.1 and emmL2.2. In addition, IgA-binding activity can be found within both types of molecules.

IN VITRO PHAGOCYTOSIS OF STAPHYLOCOCCUS AUREUS WITH SPECIAL REFERENCE TO A POSSIBLE ANTIPHAGOCYTIC FUNCTION OF COAGULASE.

Borchardt, Kenneth A. (Tulane University School of Medicine, New Orleans, La.), and William A. Pierce, Jr. In vitro phagocytosis of Staphylococcus aureus with special reference to a possible antiphagocytic function of coagulase. J. Bacteriol. 87:311-315. 1964.-Rabbit antisera were prepared to Staphylococcus aureus strains of bacteriophage types 81 and 42D with vaccines consisting of washed, heat-killed cells grown in media which either did or did not support coagulase formation. Partially purified coagulases were prepared, and were used to produce rabbit anticoagulase antisera. In vitro phagocytic studies, with the two staphylococcal strains plus rabbit polymorphonuclear peritoneal exudate cells and the various types of rabbit antisera, did not yield evidence that coagulase per se contributes to staphylococcal resistance to either ingestion or intracellular killing. The role of coagulase, if any, in the virulence of these organisms for rabbits (and probably for man) must therefore be attributed to some other mechanism.